Gas plated metal shell molds and patterns



Feb. 2, 1965 w. c. JENKlN 3,167,831

GAS PLATED METAL SHELL MOLDS AND PATTERNS Filed Dec. 11. 1961 INVENTOR W/LL/AM C. L/ENK/N WWW QM ATTORNEY5 United States Patent l 3,167,831' GAS PLATED METALSHELL MOLDS AND PATTERNS William C. Jenkin, Dayton, Ohio, assignor to Union Carbide Corporation, New York, N.Y. Filed Dec. 11, 196i, Ser. No. 158,296 2 Claims. (Cl. 22136) This invention relates to shell molds and patterns made by gas plating, and more particularly to the use of liquid heat transfer means for molds. The invention is espeeially useful in providing eflicaceous heat transfer means in mold shells and patterns such as produced by gas plating and whereby mold shapes are made of metal deposited by thermal decomposition of vaporized metal bearing compounds.

The art of gas plating to advanced to the point where it can be used to form metal shells of considerable thickness, for example to /2". One application of such metal shells is for molds, patterns and dies. For many applications, these metal shells can be backed up by a casting resin, particularly where there is littleheat to transmit or dissipate in service. Where heat must be transmitted backing of casting resin is unsuitable. For instance, in the process for making resin-bonded sand shells for casting of metals, a metal pattern used for this must be constantly kept at temperatures of 400-500" F.

Methods of backing up these metal shells with the same metal they are made of have not been very satisfactory. Such methods are, in general, expensive and in many cases the backing metal is poorly bonded to the shell. Furthermore, the shell often is distorted when the backing is applied. For these reasons, many uses of metal shell molds and patterns made by gas plating have not been possible when heat must be rapidly transmitted or dissipated. This is because of the inadequate methods of accomplishing this transmission or dissipation. It is also highly desirable that the heat transfer be accomplished in a manner that permits using conventional equipment, and making use of conventional holding devices on the usual mounting plates or areas of these machines.

In accordance with the present invention use is made of a liquid medium encased in the back of the mold cavity as shown in FIGURE 2, for the purpose of conducting away the heat.

The liquid transfer medium preferably is a metal body or mass having a relatively high heat conductivity such as the alkali metals, e.g., sodium, since no agitation is possible with the use of sealed hollow molds. Sodium metal is preferred because it has a high heat conductivity, low density and low melting point as a solid. Other metals may be used in place of sodium, e.g., potassium or lithium, or alloys of any of these metals.

While the alkali metals as aforementioned are preferred, a eutectic mixture of alkali metals may be employed as a coolant. For example, a eutectic mixture consisting of by weight 78% potassium and 22% sodium melts at l0 C. may be used. A lower cost alloy consisting of 50% potassium and 50% sodium melts at approximately 20 C. and which is liquid at normal room temperatures also is useful. A solder type alloy which has suitable heat conductivity and relatively low melting point and approaching that of the alkali metals may be tin and l2 /2% cadmium is one of the lowest melting point alloys of this type and melts at 71 C. An alloy having fairly good heat conductivity and yet a modestly deposit metal has recently 7 3,i'i,83i lratented Feb. 2, 1965 low melting point is one consisting of 31% lead, 51% tin and 18% cadmium. This alloy has a melting point of These metals, however, are not dangerous to handle, and this lower hazard in many applications will compensate for their relatively lower heat conductivity. The heat conductivity of these alloys is lower than the alkali metals and they are thus not as eflicient a heat transfer medium.

In the use of these metals per se or as alloys or eutectic mixtures as heat transfer agents as described, the metal medium must be readily castable into the mold shell and have a lower. melting point than the mold shell. ductivity with low melting pointsand are soft and weak inv the solid state. For these reasons the alkali metals have been found best and most efiicient to use as the heat transfer medium in accordance with my invention. Utilizing gas plating, the mold shell can be made of nickel, iron, cobalt or their alloys or metals of higher melting point, such as tungsten.

Unfortunately, all of the otherwise usable metals that could be cast into these shells have a higher coefficient of expansion than theaforementioned metals that are suitable for forming the shells. Some of these metals are solid at room temperature and far above, and upon heating expand and create thousands of pounds pressure per square inch which distort sthe metal shell. High melting point metals of substantial strength are therefore particularly unsuitable, e.g., copper or aluminum, which do not melt at any ordinary operating tempera ture such as the 700 F. mold temperature required for a permanent mold casting of aluminum. Low melting point alloys that possess low strength in the solid state can be used because these weak metals on expansion from heat, are themselves squeezed about in the cavity, but do not exert enough force to distort the shell.

Alkali metals, particularly sodium, are very soft at room temperature and can even be cut with a knife, and

when heated to the melting point, they do not generate high expansion pressures such as would tend to distort a metal shell mold which is filled therewith.

The use of sodium and equivalent alkali metals as a heat transfer medium in conjunction with metal shell molds and patterns formed by gas plating, as described, makes possible these hitherto impossible applications.

Employing sodium or the like alkali metal for heat transfer in connection with gas plated metal shell molds, in accordance with the present invention, makes them equivalent to solid tool steel dies in heating and in heat dissipation. In utilizing the invention, the metal shell or mold formed by gas plating is welded to a backing plate while providing a filling hole. The void between the shell and the plate is then filled by casting sodium metal through the filling hole. The filling hole is then welded shut. When the assembly is heated to the operating temperature for gas plating, e.g. 400-500 F., the sodium metal becomes molten, and functions as an excellent heat conductor. Either heating or cooling of the shell mold may be affected as required. Sodium metal has the best conductivity of the alkali metals for which this property is known, and is cheapest in cost.

In the drawings accompanying this specification, there is illustrated a shell mold having a gas plated shell and wherein the heat transfer means is illustrated as sodium metal.

FIGURE 1 is a view in elevation of a shell mold embodiment of the invention; and

FIGURE 2 is a cross-section taken on line 2--2 of FIGURE 1, and looking in the direction of the arrows.

In the drawing there is illustrated one embodiment of the invention, and comprising a metal shell foundry pat- Alkali metals have a relatively high heat con-.

tern 10, such. as maybe heated to 500 F. andiusedto make resin-bonded sand shell molds for the casting of,

metals therein. 7

.The gas plated shell llis backed by a steel plate .12.

and the interior cavity 13 is filled with sodium metal. A filling hole 14 permitsintroduction of the sodium after which the hole is plugged by a closure member 15 and welded tight as indicated at 16. In theembodiment shown, a safety] device consisting of an expansion disc 17 made of spring steel is inserted in the bottom wall, as indicated at 18, the same being suitably welded in place as shown at 19. If desired, the expansion disc. may be omitted where the volume of the filling metal is such thatit leaves a void at room temperature, but ex pands to fill it'at operating temperature.

.The use of low melting temperature alkali metals, particularly sodium, is an advantage in casting into the hollow shell, as there is no'possibility of distortion of the shell. Moreover, the metal becomes melted in the uses such metal shell molds are put to, so there is always exand backing plate which allows for a mild pressure build up, such as by inserting a metal'diaphragm in the backing plate. This diaphragm willspring slightlyso that high pressures arenot allowed to build up.

The invention hasthe .further advantage that the low density of the alkali metals results in a reduction in the weight ofthe filled shell and backing plate which isdesirable. For example, approximately as much sodium metal by weight is neededto fillthe void as would be cellent contact with the shell resulting in constantly good 1 heat transfer.

The thermal expansion of the'alkali metals or of the solder-type alloys is much greater than that of the shell and, backing plate materials which are 'madeof iron, nickel, etc., so that the volumeof metal cast into the.

void must be slightly less 'thanthat required to fill the void, leaving a small pocket of gas. Before welding the filling hole shut, or before filling the void, it is preferred practice to flush the cavity with aninert'gas. On cooling.

the alkali metal filled and sealed metal shell mold, the

metal will shrinkand create a partial vacuum.. 'On heating to a temperature above that at which it was filled, the pocket of air or gas is compressed, but to a low order of pressurethat will not damage the .mold. ..Thetpocket,. however, may at time of filling the shell mold or pattern be filled with, a gas that will slowly react with the sodium or alkali metal and thus create a high vacuum. Provision also may be made in the welded metal shell mold needed with the use of tin or lead;

What. is. claimed is:

1. A.mold 'for making gas plated metal patterns and shapes. comprising a hollow open sided metal shell formed by gas plating, a backing plate closing the open I side of said shell and welded to the outeredges thereof and thereby forming .a hollow mold, said hollow'mold being completely filled with a molten metal mass, and

said backing plate having a pressure .expansible diaphragm for'relieving expansion pressures.

2. A mold'as defined in'claim I Whe'rein the metal mass consists of sodium metal.

References Cited hythe Examiner UNITED STATES PATENTS MICHAEL 'v. BRINDISI, Primary Examiner. V

MARCUS U. LYONS, Examiner. 

1. A MOLD FOR MAKING GAS PLATED METAL PATTERNS AND SHAPES COMPRISING A HOLLOW OPEN SIDED METAL SSHELL FORMED BY GAS PLATING, A BACKING PLATE CLOSING THE OPEN SIDE OF SAID SHELL AND WELDED TO THE OUTER EDGES THEREOF AND THEREBY FORMING A HOLLOW MOLD, SAID HOLLOW MOLD BEING COMPLETELY FILLED WITH A MOLTEN METAL MASS, AND 